Disallow spaces between @, attribute name and ( in Swift 6

include/swift/AST/DiagnosticsParse.def

@@ -1510,6 +1510,13 @@ ERROR(type_attribute_applied_to_decl,none,
 ERROR(decl_attribute_applied_to_type,none,
       "attribute can only be applied to declarations, not types", ())
 
+
+ERROR(attr_extra_whitespace_after_at,PointsToFirstBadToken,
+      "extraneous whitespace between '@' and attribute name", ())
+
+ERROR(attr_extra_whitespace_before_lparen,PointsToFirstBadToken,
+      "extraneous whitespace between attribute name and '('", ())
+
 ERROR(attr_expected_lparen,none,
 "expected '(' in '%0' %select{attribute|modifier}1", (StringRef, bool))
 

include/swift/Parse/Parser.h

@@ -602,6 +602,18 @@ class Parser {
     return true;
   }
 
+  /// Consume a '('. If it is not directly following the previous token, emit an
+  /// error (Swift 6) or warning (Swift <6) that attribute name and parentheses
+  /// must not be separated by a space.
+  SourceLoc consumeAttributeLParen();
+
+  /// If the next token is a '(' that's not on a new line consume it, and error
+  /// (Swift 6) or warn (Swift <6) that the attribute must not be separted from
+  /// the '(' by a space.
+  ///
+  /// If the next token is not '(' or it's on a new line, return false.
+  bool consumeIfAttributeLParen();
+
   bool consumeIfNotAtStartOfLine(tok K) {
     if (Tok.isAtStartOfLine()) return false;
     return consumeIf(K);
@@ -1147,6 +1159,7 @@ class Parser {
 
   /// Parse a specific attribute.
   ParserStatus parseDeclAttribute(DeclAttributes &Attributes, SourceLoc AtLoc,
+                                  SourceLoc AtEndLoc,
                                   PatternBindingInitializer *&initContext,
                                   bool isFromClangAttribute = false);
 
@@ -1256,6 +1269,7 @@ class Parser {
                                         bool justChecking);
 
   ParserStatus parseTypeAttribute(TypeOrCustomAttr &result, SourceLoc AtLoc,
+                                  SourceLoc AtEndLoc,
                                   PatternBindingInitializer *&initContext,
                                   bool justChecking = false);
 

lib/ClangImporter/ImportDecl.cpp

@@ -8055,11 +8055,14 @@ ClangImporter::Implementation::importSwiftAttrAttributes(Decl *MappedDecl) {
       parser.consumeTokenWithoutFeedingReceiver();
 
       bool hadError = false;
-      SourceLoc atLoc;
-      if (parser.consumeIf(tok::at_sign, atLoc)) {
-        hadError = parser.parseDeclAttribute(
-            MappedDecl->getAttrs(), atLoc, initContext,
-            /*isFromClangAttribute=*/true).isError();
+      if (parser.Tok.is(tok::at_sign)) {
+        SourceLoc atEndLoc = parser.Tok.getRange().getEnd();
+        SourceLoc atLoc = parser.consumeToken(tok::at_sign);
+        hadError = parser
+                       .parseDeclAttribute(MappedDecl->getAttrs(), atLoc,
+                                           atEndLoc, initContext,
+                                           /*isFromClangAttribute=*/true)
+                       .isError();
       } else {
         SourceLoc staticLoc;
         StaticSpellingKind staticSpelling;